Transcript Chapter 3 ppt D
© Annie Leibovitz/Contact Press Images PowerPoint ® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College
C H A P T E R
3
Cells: The Living Units: Part D
© 2013 Pearson Education, Inc.
Cell Cycle
• Defines changes from formation of cell until it reproduces • Includes: –
Interphase
• Cell grows and carries out functions –
Cell division
(
mitotic phase
) • Divides into two cells © 2013 Pearson Education, Inc.
Interphase
• Period from cell formation to cell division • Nuclear material called
chromatin
• Three subphases: – G 1 (gap 1) —vigorous growth and metabolism • Cells that permanently cease dividing said to be in G 0 phase – S (synthetic)—DNA replication occurs – G 2 (gap 2) —preparation for division © 2013 Pearson Education, Inc.
Figure 3.31 The cell cycle.
G 1 checkpoint (restriction point) G 1 Growth S Growth and DNA synthesis M G 2 Growth and final preparations for division G 2 checkpoint
© 2013 Pearson Education, Inc.
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (1 of 6) Interphase Centrosomes (each has 2 centrioles) Plasma membrane Nucleolus Nuclear envelope Chromatin
© 2013 Pearson Education, Inc.
Cell Division
• •
Meiosis
- cell division producing gametes
Mitotic cell division
- produces clones – Essential for body growth and tissue repair – Occurs continuously in some cells • Skin; intestinal lining – None in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle • Repairs with fibrous tissue © 2013 Pearson Education, Inc.
Events Of Cell Division
•
Mitosis
—division of nucleus – Four stages ensure each cell receives copy of replicated DNA • • • •
Prophase Metaphase Anaphase Telophase
–
Cytokinesis
—division of cytoplasm by
cleavage furrow
© 2013 Pearson Education, Inc.
Figure 3.31 The cell cycle.
G 1 checkpoint (restriction point) G 1 Growth S Growth and DNA synthesis M G 2 Growth and final preparations for division G 2 checkpoint
© 2013 Pearson Education, Inc.
Prophase
• • Chromosomes become visible, each with two chromatids joined at
centromere Centrosomes
separate and migrate toward opposite poles • Mitotic spindles and asters form © 2013 Pearson Education, Inc.
Prophase
• Nuclear envelope fragments • Kinetochore microtubules attach to kinetochore of centromeres and draw them toward equator of cell • Polar microtubules assist in forcing poles apart © 2013 Pearson Education, Inc.
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (2 of 6) Early Prophase Early mitotic spindle Aster Chromosome consisting of two sister chromatids Centromere
© 2013 Pearson Education, Inc.
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (3 of 6) Late Prophase Spindle pole Polar microtubule Fragments of nuclear envelope Kinetochore Kinetochore microtubule
© 2013 Pearson Education, Inc.
Metaphase
• Centromeres of chromosomes aligned at equator • Plane midway between poles called
metaphase plate
© 2013 Pearson Education, Inc.
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (4 of 6) Metaphase Spindle Metaphase plate
© 2013 Pearson Education, Inc.
Anaphase
• Shortest phase • Centromeres of chromosomes split simultaneously —each chromatid becomes a chromosome • Chromosomes (V shaped) pulled toward poles by motor proteins of kinetochores • Polar microtubules continue forcing poles apart © 2013 Pearson Education, Inc.
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (5 of 6) Anaphase Daughter chromosomes
© 2013 Pearson Education, Inc.
Telophase
• Begins when chromosome movement stops • Two sets of chromosomes uncoil to form chromatin • New nuclear membrane forms around each chromatin mass • Nucleoli reappear • Spindle disappears © 2013 Pearson Education, Inc.
Cytokinesis
• Begins during late anaphase • Ring of actin microfilaments contracts to form cleavage furrow • Two daughter cells pinched apart, each containing nucleus identical to original © 2013 Pearson Education, Inc.
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter nuclei. (6 of 6) Telophase Cytokinesis Nuclear envelope forming Nucleolus forming Contractile ring at cleavage furrow
© 2013 Pearson Education, Inc.
Figure 3.34 Simplified scheme of information flow from the DNA gene to mRNA to protein structure during transcription and translation.
Nuclear envelope Transcription RNA Processing mRNA DNA Pre-mRNA Ribosome Nuclear pores Translation Polypeptide
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Protein Synthesis
• Occurs in two steps –
Transcription
• DNA information coded in mRNA –
Translation
• mRNA decoded to assemble polypeptides © 2013 Pearson Education, Inc.
Apoptosis and Modified Rates of Cell Division
• During development more cells than needed produced (e.g., in nervous system) • Eliminated later by programmed cell death (
apoptosis
) – Mitochondrial membranes leak chemicals that activate
caspases
DNA, cytoskeleton degradation cell death – Dead cell shrinks and is phagocytized © 2013 Pearson Education, Inc.
Apoptosis and Modified Rates of Cell Division
• • • Organs well formed and functional before birth • Cell division in adults to replace short-lived cells and repair wounds
Hyperplasia
needed increases cell numbers when
Atrophy
(decreased size) results from loss of stimulation or use © 2013 Pearson Education, Inc.
Theories of Cell Aging
• • •
Wear and tear theory
—Little chemical insults and free radicals have cumulative effects
Mitochondrial theory of aging
—free radicals in mitochondria diminish energy production
Immune system disorders
—autoimmune responses; progressive weakening of immune response; C-reactive protein of acute inflammation causes cell aging © 2013 Pearson Education, Inc.